1. Technical Field of the Invention
The present invention relates to precision measurement of polarity independent input signal by using a positive reference voltage.
2. Description of Related Art
Semiconductor applications that involve voltage specific battery management circuits critically rely on explicit measurement of an input signal and its polarity for enabling the battery charging/discharging and monitoring operation.
Precision measurement of the input signal is herein discussed with reference to the conversion of the analog voltage signal to a digital value. In an embedded system such as would include a microcontroller, an Analog-to-Digital Converter (ADC) is required to be interfaced to analog voltage sources (wherein said sources generates signals of positive and negative polarity). Conventional microcontrollers have a Successive Approximation Register (SAR) technique ADC, which does not have the capability to measure the negative voltages using a positive voltage reference. Further, the embedded ADCs do not have high resolution> It therefore becomes essential to provide an external circuit capable of measuring voltages with higher precision for both polarities of signals.
Conventional slope converters have the capability of measuring both positive and negative input signals, which requires a dual supply for measuring positive and negative input voltages. Applications based on microcontrollers, however, cannot feasibly incorporate such a dual supply.
An existing method of measuring the negative and positive voltage signals is described in U.S. Pat. No. 5,184,128, the disclosure of which is hereby incorporated by reference, which teaches an Integrating A/D converter. Herein, the input voltage polarity is first detected and is then converted to a predetermined polarity so as to have a single polarity conversion by the integral amplifier. Detection and conversion to a homogeneous polarity signal involves complex hardware incorporation in the above-described document.
Another existing polarity detection and measurement circuit is a Sigma-Delta converter, which measures differential input voltages, can also be used for measuring both positive and negative voltages. In microcontroller applications where memory size is critical, the complex digital part of sigma-delta converter is a costly solution in terms of memory size usage.
Conventional slope converters (single and dual slope ADCs) use different configurations for positive and negative input voltage signals, which are selected by using analog switches. Consequently the signals charge the capacitor in the same direction for positive and negative voltage in the same direction of polarity. However, the analog switches are not cost effective as regard to the hardware used in the polarity detection and measurement equipment.
Thus, there exists a need for an apparatus for high precision measurement of a voltage signal that does not depend on the polarity of said voltage signal. Preferably, such an apparatus would be capable of measuring the voltage signal independent of variations in the polarity. Additionally, it would be preferred if the apparatus could measure the time taken for the output signal to transit between a first level reference voltage and a second level reference voltage.